The invention relates to a reinforcing article and production of the article.
So-called 45 degree or multiaxial webs consist of two or more layers containing respective fiber segments. The fiber segments of each layer define an angle of 45 degrees with the longitudinal axis of the respective web and an angle of 90 degrees with one another. These webs find particular utility where close manufacturing tolerances, good surface quality and high shear resistance between layers are not important. Nonetheless, due to the load-bearing ability derived from their structure, they are superior to all other types of webs, as well as to nonwoven articles, especially for the reinforcement of components subjected to torsion.
Multiaxial webs currently are produced largely by stitching. Rovings (bundles of reinforcing fibers) or lengths of yarn are laid parallel to and in contact with one another in layers, and the rovings or lengths of yarn of adjoining layers are then oriented at an angle of 45 degrees to the longitudinal axis of the web and at an angle of 90 degrees to one another. Subsequently, the layers are stitched by special machines using an expensive, troublesome and slow procedure.
These multiaxial webs have voids between the rovings or lengths of yarn. Furthermore, adjoining layers cannot be properly fixed relative to one another by stitching so that they tend to shift with respect to each other. As a result, the webs cannot be punched without being destroyed (punching of the webs is essential, for example, in the manufacture of mass produced components). Moreover, the voids absorb large amounts of laminating resin thereby leading to a reduction in strength, additional weight and greatly diminished surface smoothness. A web which is free of voids and lighttight over its entire area, as required by the exacting manufacturers in high technology fields, cannot be produced by stitching. The drawbacks of webs made in this manner greatly affect the economics of the webs.
Various other methods of making webs from fibers are known. In most of these methods, discrete fibers are impregnated with a laminating resin before conversion into a web. For instance, U.S. Pat. No. 3,823,049 discloses a web containing an adhesively bound fiber network in which the fibers are not oriented at 45 degrees to an axis of the web. The Austrian patent no. 313 130 teaches a winding procedure in which individual fibers impregnated with laminating resin are wound at different angles around a core consisting of a fiber mat or staple fibers. The German publication no. 31 47 228 C2 describes a multilayered body extending along the Z-axis, that is, along a vertical axis. The body, which is produced by stitching, constitutes a rotor head for a helicopter. The body contains fibers which are inclined at 45 degrees to the Z-axis, i.e., are inclined at 45 degrees to an axis in a vertical plane rather than in a horizontal plane. The German publication no. 16 35 610 discloses a web containing a fiber network made from discrete fibers.